1. Field of the Invention
The present invention relates to a method and apparatus for detecting the presence of defects, such as particles on a substrate surface. More particularly, the invention utilizes a combination of a light source and a detector to illuminate a substrate surface and detect scattered energy therefrom.
2. Background of the Related Art
Semiconductor processing generally involves the deposition of material onto and removal (xe2x80x9cetchingxe2x80x9d) of material from substrates. Typical processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), etching and others. During the processing and handling of substrates, the substrates often become contaminated by particulates that can lodge themselves in the features of devices formed on substrates. Sources of contamination include wear from mechanical motion, degradation of seals, contaminated gases, other contaminated substrates, flaking of deposits from processing chambers, nucleation of reactive gases, condensation during chamber pumpdown, arcing in plasma chambers and so forth. As the geometries of device features shrink, the impact of contamination increases. Thus, current semiconductor manufacturing routinely includes inspection of substrates for particles to identify xe2x80x9cdirtyxe2x80x9d processes or equipment.
In general, there are two commercials methods for detecting particle contamination on a substrate surface, one being an X-Y surface scan and another being a rotary type scan. In each case, an actuating mechanism, or stage, is used to move a substrate relative to light sources, such as laser diodes. FIG. 1 is a perspective view of an exemplary inspection apparatus 10. A substrate 11 is positioned on a stage 13 capable of moving in an X-Y plane. In the case of a rotary type inspection device, the stage 13 is also capable of rotation about an axis. A light source 12 emits light beam 14 onto the substrate 11 and irradiates the surface. The light beam 14 is focused as a spot by condenser lens 15 to define an inspected area of the substrate 11. Particles, device patterns, and other protrusions on the upper surface of the substrate 11 cause the incident light beam 14 to scatter in various directions, as shown by arrows 16, according to the light incidence angle and geometry of the protrusions. The scattered light 16 is received by a collector lens 18 and then transmitted to a detector 20 positioned in proximity to the substrate 11. The detector 20 is typically a Photo-Multiplier Tube (PMT), a charge-coupled device (CCD) or other light sensitive detector. The detector 20 converts the scattered light 16 into a signal corresponding to the detected protrusions on the substrate surface. The signal is routed to a processing unit 22 to generate data regarding various parameters of interest such as the size and location of the detected protrusions. This approach, wherein scattered light from a surface under observation is detected, is known as xe2x80x9cDark Field Illumination.xe2x80x9d Dark Field Illumination implies that only light scattered by protrusions on the substrate surface is detected and light which is merely reflected by the planar substrate surface is disregarded.
One disadvantage with conventional inspection systems is the prohibitive size and cost of the systems. Current systems are typically expensive stand-alone platforms that occupy additional clean-room space. As a result of the large area, or xe2x80x9cfootprint,xe2x80x9d required by the stand-alone inspection platforms, the cost of owing and operating such a system is high. One reason for the size of the inspection systems is the desire for highly sensitive equipment capable of detecting sub-micron particles. In order to achieve such sensitivity, vibration due to the various moving components of the platform such as the stage, which interfere with the inspection techniques, must be eliminated. Thus, the inspection platforms are stabilized using a massive base comprising, granite slab, for example, to minimize the effects of vibration. To accommodate the wide range of motion of the stage and the massive base, conventional platforms occupy a large footprint in a fabrication facility (fab), thereby increasing the cost of operation of the overall fab.
Another problem with current inspection devices is the negative impact on throughput, or productivity. As described above, a stage moves a substrate through an X-Y plane to position the substrate relative to the light source. Conventional inspection platforms, such as the one in FIG. 1, illuminate only a small portion, or spot, on the substrate being inspected. The substrate is then moved repeatedly by the stage to expose the entire surface of the substrate to the light source. Consequently, conventional platforms drastically increase overhead time associated with chip manufacturing. One attempt to reduce the overhead time and increase throughput in a reticle inspection using a stage is shown in U.S. Pat. No. 5,663,569 which utilizes optics capable of shaping the light beam into a line, or slit, to allow for single-pass inspection. The slit dimensions are adjusted to accommodate the width of the object under inspection so that the object need only be scanned in a single direction once. However, the light source is positioned to obliquely irradiate the reticle, thereby producing a non-uniform spot pattern. Specifically, the light source is offset to one side of the reticle such that the reticle moves past the light source during a scan as opposed to toward or away from the light source. As a result, the light produces a more intense pattern on the portion of the reticle closer to the light source while a less intense pattern is produced farther away from the light source.
Throughput is farther diminished because the current inspection systems are standalone platforms that require substrates to be removed from the vacuum environment of the processing system and transferred to the separate inspection platform. Thus, production is effectively halted during transfer and inspection of the substrates. Further, because such an inspection method is conducive only to periodic sampling due to the negative impact on throughput, many contaminated substrates are processed before inspection and detection of problems occurs. The problems with substrate inspection can be compounded in cases where the substrates are re-distributed from a given batch making it difficult to trace the contaminating source.
It would be preferable to have an inexpensive in situ inspection method and apparatus incorporated into existing processing systems capable of detecting particles on substrates. Further, the preferred inspection apparatus should be capable of being retrofitted to existing processing systems. The inspection apparatus should be positioned to allow inspection of each substrate before and/or after processing. Impact to throughput should be minimized by inspecting substrates xe2x80x9con-the-flyxe2x80x9d during transfer between typical processing steps without the need for a separate inspection platform and stage.
Another problem with particle detection systems is the noise produced by chip patterns formed on substrates. During inspection by conventional illumination techniques, the patterns act as micro-mirrors causing the light to reflect in various directions. As a result, the patterns may produce misleading information, i.e., the patterns may indicate the presence of foreign particles where none are found. In order to allow particle detection of patterned substrates various methods and apparatus have been implemented in the art. U.S. Pat. No. 5,463,459, entitled xe2x80x9cMethod and Apparatus for Analyzing the State of Generation of Foreign Particles in Semiconductor Fabrication Process,xe2x80x9d provides a method of detecting foreign particles on a substrate by xe2x80x9celiminatingxe2x80x9d the patterns formed on the substrate. For example, corresponding portions of adjacent chips are compared to determine differences. The chips are illuminated with a light source to cause reflection of the light which is detected by detection equipment while the substrate is actuated by a conventional stage. The reflected distribution of light is then compared to determine the presence of foreign particles on the substrate. The portion of the resulting signals which are identical are erased leaving only differences in the signals. The differences are assumed to be the result of particles on the substrate.
While such a method can achieve relatively high resolution capable of detecting sub-micron particles, the necessary equipment and signal processing systems are complex and expensive as well as time-consuming because in order to produce high resolution detection long scanning times are needed. Further, sources of foreign particles can produce large-scale particles, therefore, small-scale particle detection may not be necessary in cases where catastrophic chamber failures occur. By xe2x80x9ccatastrophicxe2x80x9d is meant flaking of material that has accumulated on the chamber surfaces.
Therefore, what is needed is a system capable of rapidly determining the condition of a substrate in order to facilitate a subsequent substrate handling decision. That is, a preferred detection system would allow a quick decision to be made about whether an additional and more precise particle detection analysis is necessary. Preferably, the system would also allow the substrate inspection to be performed on-the-fly and produce real-time data on each substrate undergoing processing, rather than just arbitrarily selected substrates from a batch. Such a preferred system would maximize the system throughput and reduce operating costs by eliminating the need for time-consuming inspection of small-scale particles and also the cost associated therewith.
Therefore, there is a need for an integrated particle detection system which allows for on-the-fly monitoring and the detection of particles in a processing system.
The present invention generally provides a particle detection apparatus in a processing system. In one aspect of the invention, a transmitter unit and a receiver unit are disposed on or near a chamber and cooperate to transmit and detect energy. The transmitter unit is positioned to transmit a signal onto a moving substrate surface. The receiver unit is positioned to collect a scattered portion of the signal and direct the same to a processing unit.
In another aspect of the invention, a transmitter unit and a receiver unit are disposed on a semiconductor processing system and cooperate to transmit and detect energy, respectively. The transmitter unit is positioned to transmit a signal into a region of the processing system, such as a transfer chamber, and onto a substrate surface moving therethrough. In one embodiment, the signal is transmitted onto a substrate moving through a cavity of the transfer chamber and preferably between the transfer chamber and an adjacent vacuum chamber. A robot preferably located in the transfer chamber or a front-end environment of the processing system, enables movement of the substrate. The receiver unit is disposed to collect a scattered portion of the signal and direct the same to a processing unit. Preferably, the transmitter unit and the receiver unit are disposed in a region external to the processing system.
In yet another aspect of the invention a light source and one or more charge-coupled devices (CCD) are disposed on or near a chamber and cooperate to transmit and detect energy, respectively. The laser source; is positioned to transmit a signal onto a moving substrate surface. The CCD is disposed to collect a scattered portion of the signal and direct the signal to a processing unit.
In still another aspect of the invention, a signal is transmitted on a substrate moving in a first direction between a first vacuum chamber and a second vacuum chamber of a semiconductor processing system or rotationally within the first chamber. Preferably, the first vacuum chamber is one of a transfer chamber or a front-end environment and the second vacuum chamber is one of a process chamber, a service chamber or a load lock chamber. A reflected portion of the signal is received by a receiver unit and subsequently directed to a processing unit for processing. In one embodiment, the reflected portion of the signal is reflected by particles disposed on the substrate. In another embodiment, the reflected portion of the signal is reflected by alphanumeric characters disposed on the substrate.
In still another aspect of the invention, a signal is transmitted on a substrate moving in a first direction between a first and second vacuum chamber of a semiconductor processing system or rotationally within the first chamber. Preferably, the first vacuum chamber is one of a transfer chamber or a front-end environment and the second vacuum chamber is one of a process chamber, a service chamber or a load lock chamber. A reflected portion of the signal is received by a receiver unit and subsequently directed to a processing unit for processing. The processing unit is adapted to read a computer-readable program product to generate information pertaining to the substrate. Preferably, the program product is adapted to provide substrate positional information, substrate reflectivity information, specular information, substrate defect information, substrate damage information, particle contamination information for the substrate support member and a substrate disposed thereon, alphanumeric character information, robot behavior information, calibration information for a robot, a transmitter unit and/or a receiver unit, and any combination thereof.
In still another aspect of the invention, a method of determining the center and/or orientation of a substrate is provided. A substrate is positioned in a chamber having a receiver unit and transmitter unit disposed therein. The surface of the substrate is illuminated with radiation from the transmitter unit and an image representative of at least an edge portion of the substrate is captured by the receiver unit. The image is analyzed to determine at least one of the center or orientation of the substrate. The substrate surface illuminated may be the backside of the substrate or the upper surface of the substrate in facing relation to the receiver unit.